Light reflectors



y 14, 1957 H. A. DOOLITTLE ETAL 2,791,938

LIGHT REFLECTORS Filed May 1'7 1949 United States Patent LIGHT REFLECTORS Harold A. Doolittle, Chicago, and Sidney A. Heenan,

Oak Park, 11]., assignors to Electric Stop Nut Corporation of America, Union, N. J., a corporation of New Jersey Application May 17, 1949, Serial No. 93,658

1 Claim. (Cl. 88-78) The present invention relates to light reflectors and has particular reference to such reflectors in the form of individual units used on automotive vehicles separately or in conjunction with other lights as warning devices, as highway delineators and in the fabrication of highway, advertising and other forms of signs. Still more particularly the invention relates to units of such character presently molded from thermoplastic. material and capable of being molded. from thermosetting material, such materials hereinafter being referred to generically as synthetic plastics.

For many years units of the kind to which the invention relates have been used in a widevariety of specific applications which in the main involve outdoor installations where the units are exposed to the elements and where moreover they must function without material impairment of their reflecting efficiency over a period of years. In order to do this it is obvious that the light reflecting face of the unit, which ordinarily consists of a multiplicity of individual surfaces, must be kept clean and free from deposits both of solid matter, such as dust, and also of fluid deposits, such as condensation of moisture from the ambient atmosphere.

Units of the kind under consideration were first made of glass, until more recently it was found that more efiicient reflectors could be made from thermoplastic material, particularly methyl methacrylate (sold under the tradenames Lucite or Plexiglas), the latter to a considerable extent having replaced glass for the purpose. In either case, however, the general practice'in the past has been to provide the reflector element with a metallic backing plate crimped or otherwise secured to the perimeter of the reflector element together with a suitable gasket intended to provide a hermetic seal for the protection of the reflecting face of the element. Experience has proved, however, that this construction for one or another reason, fails to provide a reliable hermetic seal that can be relied upon to endure under the conditions which are encountered in usual use. Subsequent. to the advent of thermoplastic elements, the former metal backing arrangement has been improved upon by the use of backing plates made of thermoplastic material, preferably the same as that of the reflector element, and heat sealed thereto to provide the desired hermetically sealed unit. Such a construction has proved to be commercially satisfactory from the standpoint of performance, but is relatively expensive from the standpoint of the additional amount of the more expensive thermoplastic material required to be used and also from the standpoint of cost of production, since the heat seaiing operation is a delicate one and not well adapted to speedy mass production methods at very low costs.

It is, accordingly, the general object of thepresent invention to provide a new and improved form of reflector unit, which will be of permanently hermetically sealed character and which can also be much more readil and cheaply produced than such units have heretofore been 2,791,938 Patented May 14, 1957 made. Other and more detailed objects of the invention, together with the advantages to be derived from its use, will appear more fully as the ensuing portion of this specification,taken in conjunction with the accompanying drawings, proceeds.

In the drawings:

Fig. 1 is a plan view of a reflector unit embodying the invention;

Fig. 1a is a section taken on the line la-la of the unit shown in Fig. 1;

Fig. 2 is amore or less schematic view of apparatus for making units of the kind shown in Fig. 1;

Fig. 3 is a section on larger scale of the rolls shown in ice 'Fig. 2; and

Fig. 4 is a more or less diagrammatic section showing suitable means for making double reflector units.

Referring now more particularly to Figs. 1 and la, the reflector element 10 shown is of the usual button or disc form, although it is to be understood that this form is shown by way of example only and that insofar as this invention is concerned the contour of the perimeter can be of any desired configuration, such as any of the geometric figures, or a letter, numeral or arbitrary fanciful design.

For the purposes of the present invention the material is a light transmitting synthetic plastic, advantageously methyl methacrylate, such light transmitting material hereinafter for convenience being referred to as transparent, the term transparent being understood to include non-opaque materials of colored, translucent and like nature.

As seen from the figures the element 19 has an obverse light receiving face 12 and a reverse light reflecting face 14 comprising a multiplicity of prismatic reflecting surfaces 15. While the specific nature and configuration of the reflecting face is not controlling so far as this invention is concerned, a preferred form is that which is disclosed in U. S. Patent 2,022,639 granted November 26, 1935 to Jonathan C. Stimson, the characteristic of which is that within the intended included angle of use, light from any given source impinging the reflector is reflected back to the source.

Preferably, as shown, the element 10 is slightly dished to provide a convex obverse face 12 with respect to which the reverse face 14 is concave and generally parallel to provide a wall of generally uniform average thickness. The perimeter of the element It is formed to provide a rim 16 having a face 18 the plane of which is advantageously but not necessarily spaced from the reverse face M to provide a cavity 29 between the latter face and the plane of the face 18. y

it is of course the face 14 with its reflecting surfaces that must be hermetically sealed from the ambient atmosphere if a satisfactory device is to be obtained and in accordance with the present invention this is accomplished by providing a backing member 22 comprising a thin metallic foil 24 coated with a film of synthetic plastic material as which may or may not be of the same composition as the element 10 but which is capable under the influence of heat and sufficient pressure to insure good contact of forming a fusion bond with the material of the element ill, to the rim face 18 of which it is fused.

Many different specific materials and combinations of materials may be employed in the fabrication of the backing member. Advantageously, however, the metal foil employed is of a relatively soft non-ferrous metal such, for example, as lead or aluminum. The film or coating may be any suitable composition which, as noted above, is capable of fusion bonding under heat and contact pressure with the material of' the reflector element. Also, in addition to the metal foil and thermoplastic coating, the backing member may for reasons of mechanical strength andprotection of the metal from the atmosphere have a reinforcing backing element such, for example, as bitumenimpregnated Kraft paper or the equivalent. From a cost standpoint and also in order to secure the best results it is desirable that both the foil and the coating of plastic material be very thin. Such composite materials of metal foil with a heat sealable coating, with or without a further backing reenforcing element, are well known for the purpose of packaging articles for shipping to protect them against damage by the atmosphere.

From actual experience we have found that when used in conjunction with reflector units made of Lucite, backing members comprising lead foil .001 thick, reinforced with asphalt and Kraft paper and coated with polyvinyl butyral .002 thick are highly satisfactory for the purposes of the present invention. Satisfactory coating of the foil with plastic material may be accomplished merely by spraying a diluted solution of the plastic material in a suitable volatile solvent onto the face of the foil, with the coating preferably made uniform by passing the foil under a doctor blade, the evaporation of the solvent leaving a coating on the foil and adhering to the latter only through a mechanical contact bond.

Obviously, many other materials may be used so long as they meet the fusion bonding requirements and do not release, when heated, decomposition vapors that will attack the reflecting surfaces. In many instances it may be most desirable to have the coating on the backing member of the same material as that of the reflector to which it is to be sealed.

The assembly of the reflector and backing member to form a hermetically sealed unit is very readily and easily accomplished. We have found that with a backing member made of the materials given in the example above and heated to 240 F. by being placed on a hot plate, hermetic fusion bonds which proved to be leak-proof under test, were obtained merely by placing a Lucite reflector on the heated backing member with only sufiicient pressure to ensure good contact between the backing member and the rim of the reflector and with the parts maintained in contact while heat was applied for only a matter of a very few seconds, for example two to five seconds.

Experience has shown that metal foil alone cannot be fused as a practical matter to the thermoplastic reflector material and even were such the case a reliable hermetic seal is not obtainable with the very thin metal foil contemplated by the present invention since such thin foil is to a greater or lesser extent porous.

One of the principal problems of producing articles of the kind under consideration is the fact that if the reflector is to be efficient as a light reflecting medium, great exactness of the light reflecting surfaces is required and the Stimsonite reflectors as manufactured today are products of molding operations of the greatest exactitude and precision. The requirement for great precision renders the problem of heat sealing reflectors to backing members and the like one of considerable difliculty since application of heat to the reflectors of suflicient intensity to cause fusion is most likely to cause warping or distortion of the thermoplastic material or even sufficient softening to destroy the precision of the reflecting surfaces if heat of such intensity is applied for any material length of time.

By utilizing very thin metal foil, preferably of the kind having a relatively high rate of heat conductivity, and a very thin film or coating of heat scalable plastic material on the foil, We are enabled to effect a hermetic seal between the backing member and the reflector by the application of heat for only a very short period of time. Even with an extremely short period for application of heat uniformity of-sealing is obtained, largely we believe due to the rapidity of conduction of the heat through the thin foil so that even distribution of heat is obtained. Not only does such time of application of heat avoid supplying so much heat that the reflector may be overheated during the heating operation, but the total quantity of heat transmitted to each reflector is so small that no ill effects result from heat flow by conduction from the surface which is heated to fusion temperature into the body of the material before the unit cools by radiation to a normal temperature. Obviously, one of the principal factors contributing to the small amount of heat required is the employment of very thin foil the mass of which is such that a very small amount of heat quantitatively is required to bring the metal up to the fusion temperature of the plastic material.

The fusion point which is obtained may, depending upon the materials used, result from surface or skin melting of either one or both of the materials of the reflector element and the coating on the backing member. This, however, is immaterial so long as a fusion bond is obtained.

The use of the metal foil also enables high frequency induction heating to be employed to advantage in many v instances instead of applying heat by conduction from a heating element.

One of the requirements for articles under consideration is low cost and in accordance with the present invention reflector units can be very rapidly and cheaply made by means of apparatus such for example as is illustrated in Figs. 2 and 3 of the drawings.

In the embodiment shown a plate 28 provides a heating zone and which by any suitable means may be heated to the desired temperature as for example by means of a resistance coil indicated at 30. A strip 32 of backing material from a roll 34 is drawn through the heating zone with the thermoplastic coated side of the strip uppermost by means of a pair of feed rolls 36 driven in any suitable manner. Rolls 36 have rims 38 engaging the strip 32 on opposite sides and are provided with central grooves 40 to permit the passage of the reflectors. A series of individual reflector elements 10 are fed onto strip 32 in advance of the heating zone, either by hand or by any suitable feeding mechanism of which there are many known varieties. In many instances the weight of the reflector elements may be alone sufficient to insure suitable contact between the rims of the elements and the strip of backing material but additional pressure may if desired be applied as for example by means of an endless belt 42 of any suitable flexible material which may itself be of a plastic nature. Belt 42 runs over pulleys 44 and as shown is relatively loose so that the portion of the belt running below the pulleys rests on the reflectors to provide the desired contact pressure due to the weight of the belt. Obviously the amount of pressure may be varied through choice of the material of which the belt is formed and the belt may obviously if desired be additionally weighted. The belt 42 should run concurrently with the strip 32 and to this end one of the pulleys may advantageously be driven in synchronism with the feed rolls although in some instances a separate drive for the belt may not be required, since if the inertia is small the frictional contact between the belt and the reflector elements and between the latter and the strip 32 may be sufficient to actuate the belt.

The fusion seal between the reflector elements and the backing strip is effected during the passage of the reflectors through the heating zone and after the strip has been delivered from the feed rolls the strip may then be severed in any desired manner to provide the individual reflector units having the backing member trimmed to the desired contour. Such a severing arrangement is indicated diagrammatically by the supporting plate 46 and the reciprocating cutter 48. Obviously any desired form of severing mechanism may be employed or if desired it may be done by hand.

While for purposes of illustration the heating zone has been illustrated as activated by a contact heating plate it will be apparent that heating of the elements passing through the zone may equally well be effected through the medium of suitable high frequency induction heating effected through elements of well known kind.

In many cases so-called two-way reflector units are desired, that is, units capable of reflecting light from either of two opposite directions, and the present invention lends itself particularly Well to the production of such units. To produce such units it is advantageous to provide a backing material having a metal foil coated on both sides with a film of thermoplastic and apply heat to the backing member with two reflector elements in contact with opposite faces of the backing member in back-to-back relation.

In Fig. 4 there is diagrammatically illustrated suitable means for effecting such an assembly. The means illustrated in this figure comprises a supporting die or block 50 having a rim 52 around a center recess 54 for supporting the rim portion of a reflector element over which is placed the backing element 56 coated on both sides with films of thermoplastic material. Over the backing member 56 a second reflector element 10 is placed and is engaged by means of a flange or a ram 58 having a flange 60 engaging the rim of the reflector. While either one or both of the elements 50 or 58 may be heated to provide conduction heating elements, the arrangement shown is particularly well adapted for the use of high frequency induction heating which operates to heat the foil and possibly the heat sealable coating, by reason of their electrical properties without a corresponding rise in temperature of the material of the reflectors, the heat thus applied being rapidly conducted across the surfaces to be sealed by conduction of the metal of the foil.

In certain instances where induction heating is employed, it may be possible to dispense with metal foil and employ other material, which has electrical properties different from those of the heat sealable film, for supporting the latter. Where two reflectors are in back-to-back relation, a film of heat sealable plastic material alone may act both as the source of heat and the bonding agent, when inductively heated.

From the foregoing it will be evident that within the scope of the invention many specific materials and combinations of material may be employed and that many different specific temperatures, times of heating, etc., may be used depending upon the specific nature of the materials used. Also, as has previously been pointed out the invention is applicable to a wide variety of forms and configurations of reflecting elements which may or may not be combined with other optical surfaces, such for example as a lens surface on the obverse face of the element or variations in the reverse face of the element.

The invention is accordingly to be understood as embracing all articles falling within the scope of the appended claim.

What we claim:

A light reflecting unit comprising a rigid element of light transmitting synthetic plastic material having an obverse light receiving and transmitting face, a reverse face comprising a plurality of light reflecting surfaces and a rim encompassing said reverse face, and a backing member extending across the reverse face of said element in spaced relation to said light reflecting surfaces and joined to said rim around the perimeter thereof to provide a gaseous fluid filled cavity between the reverse face of said element and said backing member, hermetically sealed off from the ambient atmosphere, said backing member comprising a metallic foil having a thin film-like coating of heat sealable synthetic plastic material fusion bonded to said rim to provide said hermetic seal.

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